1. Technical Field
The present invention relates to a circuit, system, and method for degradation detection, and particularly to a degradation detection circuit in a MOS (Metal Oxide Semiconductor) transistor, degradation detection system and degradation detection method using the degradation detection circuit.
2. Background Art
The MOS transistors are often used in integrated circuits, such as a microprocessor. The MOS transistor is mainly used as a switch to compose various logic circuits. In order to perform delay design in an integrated circuit, it is necessary to take into consideration the delay generated in a MOS transistor. Repeated operation of the MOS transistor causes degradation, and the degradation generates longer delay. Therefore, the delay design of the integrated circuit which includes the MOS transistor has been taking into consideration the lifetime degradation of the MOS transistor as a delay margin. Accordingly, the MOS transistor that operates at a faster operating frequency than the operating frequency required for the integrated circuit has been preventing performance degradation in the entire integrated circuit even when a delay is generated by degradation. However, nowadays, owing to the improvement in the operating frequency and performance required for the integrated circuit, it is necessary to adopt a MOS transistor that has an operating frequency faster than the MOS transistor with consideration over the delay margin.
Japanese Unexamined Patent Application Publication No. 11-27128 discloses a technique regarding a semiconductor integrated circuit which can prevent in advance an operation shutdown of the entire system by evaluating the characteristic degradation in a semiconductor integrated circuit apparatus while mounting a degradation detection circuit on a system and operating the degradation detection circuit. To be specific, the semiconductor integrated circuit disclosed in Japanese Unexamined Patent Application Publication No. 11-27128 uses a transistor for evaluation that degrades under equivalent conditions as the transistor used for normal operations. The semiconductor integrated circuit can further detect the extent of the transistor degradation based on the amount of change in the threshold voltage of the transistor for evaluation. This enables easy detection of a transistor before a failure occurs. Moreover, by the detection of the transistor before being failed, it is possible to perform an action such as replacement, thereby avoiding a sudden system failure.